乒乓比賽【樹狀數組】

樹狀數組水題

#include <bits/stdc++.h>
#define sc(x) scanf("%d",&x)
using namespace std;
const int maxn = 20006;
const int maxm = 1e5+50;
typedef long long ll;
int n;
int a[maxn];
int bit[maxm];
int rbit[maxm];
int c[maxn],d[maxn];
int lowbit(int t) {return t&(-t);}
void add(int i,int m)
{
    while(i<maxm)
    {
        if(m==1)
        bit[i]++;
        else rbit[i]++;
        i+=lowbit(i);
    }
}
int sum(int i,int m)
{
    int s=0;
    while(i>0)
    {
        if(m==1)
        s+=bit[i];
        else s+=rbit[i];
        i-=lowbit(i);
    }
    return s;
}

int main()
{
    int T;
    sc(T);
    while(T--)
    {
        sc(n);
        memset(bit,0,sizeof(bit));
        memset(rbit,0,sizeof(rbit));
        memset(c,0,sizeof(c));
        memset(d,0,sizeof(d));
        ll all =0;
        for(int i=1;i<=n;i++) sc(a[i]);
        for(int i=1;i<=n;i++)
        {
            add(a[i],1);
            c[i] = sum(maxm-1,1)-sum(a[i],1);
            //cout<<c[i]<<endl;
        }
        for(int i=n;i>=1;i--)
        {
            add(a[i],2);
            d[i] = sum(maxm-1,2)-sum(a[i],2);
        }

        for(int i=1;i<=n;i++)
        {
            all += (ll) c[i] * (n-i-d[i]);
            all += (ll)(i-1-c[i])*d[i];
        }
        printf("%lld\n",all);
    }
    return 0;
}